Chemical Modification of Buildup Epoxy Surfaces for Altering the Adhesion of Electrochemically Deposited Copper

Abstract

The adhesion of electrochemically deposited copper on top of chemically surface modified epoxy layers for buildup purposes is examined. Using a wet-chemical surface synthesis reaction iminodiacetic acid, imidazole, and mercaptopyrimidine groups were chemically imprinted on the surface of buildup epoxy layers based on nucleofilic substitutions. The synthesis was followed by an identical electroless Cu deposition and peel strength measurement sequence. The identity of certain groups at the surface has pronounced influence on the adhesion strength of electrochemically deposited metals and is compared with traditional swell/ oxidation treatments of the surface of the polymer. By varying the identity of the chemical groups at the surface, the chemical part of the adhesion can be altered. The changes in roughness of the polymer surface were minimized by choosing solvents that exhibit minimum diffusion into the polymer and by limiting the reaction temperature. In this way the changes in the physical part of adhesion could be kept to a minimum. The chemical composition of the surface is examined by attenuated total reflection-infrared and X-ray photoelectron spectroscopy measurements. Weight changes were recorded after each separate wet-chemical treatment. Surface synthesis influences the peel strength negatively or positively and modifies the deposition rate and etching speed of electrochemically deposited copper.The surface properties of the polymer obviously have a big impact on the adhesion strength of electrochemically deposited metals on epoxy polymers used for buildup purposes. By chemical treatment the characteristics ͑physical and chemical͒ of the polymer surface can be changed in order to improve adhesion. Hence there is intense recent research into improving the adhesion of plated copper onto polymer surfaces. A number of publications 1-6 exist on surface treatments with wet chemicals to improve adhesion strength of electrochemical deposited copper on polymers.The study of the mechanisms of adhesion uses various concepts, emphasized by the fact that many theoretical models of adhesion have been proposed. These theories are both complementary and contradictory. 7 The five theories used are mechanical interlocking, electronic theory, the theory of boundary layers and interfaces, adsorption ͑thermodynamic͒ theory, and chemical bonding theory. 7 All theories consider two parts of adhesion: The physical or mechanical part of adhesion, which is linked to the roughness of the interface, and the chemical part of adhesion, caused by the interactions between the materials of both layers.The mechanical interlocking theory, proposed originally by MacBain and Hopkins, 8 conceives of mechanical keying or interlocking of one substance into cavities, pores, and asperities of the other material to be the major factor in determining adhesive strength. However, the possibility of establishing a good adhesion between smooth surfaces leads to the conclusion that the theory of mechanical keying cannot be universal. To overcome this...

Electroless Copper Deposition Using Sn/Ag Catalyst on Epoxy Laminates

“…4,[14][15][16]41 Seeding of the tin/palladium catalytic colloid onto the epoxy surface is accompanied by an increase in surface roughness in the swelland-etch process. 7,8,17,21,24 In contrast, the surface was not appreciably roughened by the H 2 SO 4 pretreatment, even for over-treated surfaces, as shown in Figure 2. The results also show that the H 2 SO 4 pretreatment produced a unique surface for catalyst seeding, which was not recreated by other strong acids, HCl and H 3 PO 4 .…”

“…7,8,[17][18][19][20][21] Mechanical adhesion is based on the increase of the surface in surface area due to roughness from micropores, cavities and asperities on the substrate surface. 8,18,21 Generally, the higher the surface roughness, the higher the adhesion strength. The higher surface roughness leads to greater contact area between the epoxy laminate substrate and the metal as well as the catalyst.…”

“…alkaline KMnO 4 ) oxidizes the polar groups and forms functionalities such as carboxylic acid, ketones, and aromatic alcohols, and breaks ether bonds in the epoxy, creating micropores and cavities. 7,21,36 Although the effect of the oxidizer is isotropic in nature, the heterogeneous distribution of polar groups on the epoxy surface and within the near-surface region leads to different etch rates at the various sites. The etch rate is higher in regions where there is a high concentration of polar groups which leads to an increase in surface roughness.…”

Adhesion and Reliability of Anisotropic Conductive Films (ACFs) Joints on Organic Solderability Preservatives (OSPs) Metal Surface Finish

“…14 In addition, it is also reported that the benzimidazole can improve the adhesion between polymeric materials such as epoxy or polyimide, and copper. 15,16 Generally, imidazoletype curing agents are widely used for epoxy curing. The chemical structure of the OSP material (benzimidazole) is also based on the imidazole system.…”

Effects of metal surface finish on the anisotropic conductive adhesives (ACAs) joints

“…Song et al reported that polymeric adhesion promoter, polybenzimidazole, which was the base OSP material, showed better adhesion strength because polybenzimidazole prevented the surface of copper from oxidation [8]. Besides, some reseachers reported that the benzimidazole could improve the adhesion between polymeric materials, such as epoxy or polyimide, and copper [9][10]. Generally, imidazole type curing agents are widely used for the epoxy curing and the reaction between benzimidazole in OSP and ACF can enhance the adhesion strength.…”